The present invention relates to a device for switching the diameter of a scanning beam in response to a selection of the number of scanning lines of a picture image scanning and recording apparatus.
In graphic art processing, since a secondary copy for printing form, or a printing plate prepared from a copy by means of a photographic system using a camera requires great difficulty in making a correction to reproduce contrast of a picture image on the copy as it is or to emphasize its details, the picture image scanning and recording apparatus (hereinafter referred to as "scanner") easily enables such correction in a desired manner by operating an electronic circuit, has come to be increasingly used.
Although it has been conventionally regarded as difficult in this kind of scanner, particularly in a scanner of a mechanical plane system, to increase processing speed, an adoption of polygon mirror scanning and galvano mirror scanning has solved the foregoing difficulty. With the expansion of using such scanning methods, advantages obtained by above-mentioned reproduction of tone and emphasis of details are utilized efficiently, so that, in addition to a scanner for a screen with comparatively rougher lines which has been hitherto used mainly for preparation of secondary copy for the newspaper, a scanner capable of giving rise to a number of finer scanning lines has been demanded, with increasing tendency to use graphic printing more frequently.